The following is a list of dates obtained since the compilation of List XI in December 1965. The method is essentially the same as described in that list. Two CO2-CS2 Geiger counter systems were used. Equipment and counting techniques have been described elsewhere (Crane, 1961). Dates and estimates of error in this list follow the practice recommended by the International Radiocarbon Dating Conferences of 1962 and 1965, in that (a) dates are computed on the basis of the Libby half-life, 5570 yr, (b) A.D. 1950 is used as the zero of the age scale, and (c) the errors quoted are the standard deviations obtained from the numbers of counts only. In previous Michigan date lists up to and including VII, we have quoted errors at least twice as great as the statistical errors of counting, to take account of other errors in the over-all process. If the reader wishes to obtain a standard deviation figure which will allow ample room for the many sources of error in the dating process, we suggest doubling the figures that are given in this list.

We wish to acknowledge the help of Patricia Dahlstrom in preparing chemical samples and David M. Griffin and Linda B. Halsey in preparing the descriptions.

The requests to measure many samples, and samples with very low carbon masses, make it necessary to develop new techniques in sample handling to accelerate sample preparation and to eliminate carbon contamination. Our 40 MC-SNICS was recently modified to a hybrid ion source. To run the hybrid ion source with a gas parameter, settings were studied and a gas handling system for the direct coupling of an elemental analyzer and a gas ion source was developed.

We consider a general methodology for the transferral of chronologies from a master reference record containing direct dating information to an undated record of interest that does not. Transferral is achieved through the identification, by an expert, of a series of tie-points within both records that are believed to correspond to approximately contemporaneous events. Through tying of the 2 records together at these points, the reference chronology is elastically deformed onto the undated record. The method consists of 3 steps: creation of an age-depth model for the reference record using its direct dating information; selection of the tie-points and translation of their age estimates from the reference to the undated record; and finally, creation of an age-depth model for the undated record using these uncertain tie-point age estimates. Our method takes full account of the uncertainties involved in all stages of the process to create a final chronology within the undated record that allows joint age estimates to be found together with their credible intervals. To achieve computational practicality, we employ a Gaussian process to create our age-depth models. Calculations can then be performed exactly without resort to extremely slow Monte Carlo methods involving multiple independent model fits that would be required by other age-depth models.

Pollen analysis as well as 18O/16O results on lake marl show that the Younger Dryas climatic period, between about 11,000 and 10,300 bp, was the last vigorous cold phase of the Würm Glacial. Detailed 14C analyses from a peat bog near Wachseldorn (Switzerland) point to a 14C anomaly in this period. Further indication of a 14C anomaly is given by the observation that, during the Younger Dryas period, the sedimentation rates in several lakes apparently were higher than in adjacent periods; an explanation might be that the 14C time scale was compressed between 11,000 and 10,000 bp, ie, the atmospheric 14C/C ratio varied. If real, this suggested 14C variation would probably be connected to the climatic events during this transition period from Later Glacial to Postglacial.

During Pleistocene pluvial precipitation was sufficient for the maintenance of groundwater supported lakes and for the accumulation of playa lakes in wind-scoured depressions during the early Holocene pluvial. At places where ground water reaches near to the surface, wells (birs) have been dug and maintained in historic times. These birs have been used as sampling sites for water analyses, including carbon-14 levels, carbon and oxygen stable isotope ratios, tritium concentrations, and chemical data.

All the waters from birs analyzed to date produced apparent radiocarbon ages ranging from late historic to early Holocene, and tritium analyses on some of these indicate no recharge during the Atomic age.

Sources of error for the radiocarbon analyses, including exchange with atmospheric CO2, respiration by plant roots, and contact with carbonates of considerably older age, were evaluated. None of these factors have such an extreme impact on the measurements as to render the result invalid. Two trends revealed by these data are an increase in apparent age from northwest to southwest and with subsequent extractions at the same site where the hand-dug well was bailed out and sampled four times within two days.

We conclude that recharge of shallow ground water occurred in early Holocene time, and some recharge of deeper aquifers may have occurred where infiltration paths permitted. Some recharge occurred in late Holocene (post pluvial) time, but the net trend has been toward hyper-aridity that characterizes the area today.

Accelerator mass spectrometry (AMS) radiocarbon dates were obtained for 18 mollusk shells collected alive along the Buenos Aires province coast, Argentina, over the period AD 1914–1935. Reservoir ages were estimated for all samples on the basis of the tree-ring calibration curve for the Southern Hemisphere (SHCal04, McCormac et al. 2004) and the marine δR values calculated as the difference between the conventional 14C age and the age deduced from the marine, mixed-layer model calculation (Marine04, Hughen et al. 2004). For most coastal locations, a great δR scatter was observed, ranging from 191 to 2482 yr, which is explained by the input of varying content of dissolved carbonate by rivers and groundwater (“hardwater effect”) and indicates a serious limitation for shell-based 14C chronologies. Within the interior of Bahía Blanca estuary, δR values ranged from −40 to 50 ± 46 as a consequence of the local geological particularities of the environment. This suggests that, with some restrictions, the marine calibration curve with standard parameters (δR = 0) could be used at this location.

A variety of physical and chemical techniques are used to fractionate soil organic matter, but detailed comparisons of the different approaches and tests of how separation methods influence the properties of isolated organic matter pools are lacking. In this case study based on A horizon samples of 2 California coniferous forests soils, we 1) evaluate the effects of root removal and ultrasonic dispersion on the properties of the <2 g cm-3 light fraction and 2) compare the properties of fractions obtained by sequential density separations of ultrasonically treated soil with those obtained by density followed by acid/base hydrolysis (Trumbore et al. 1996).

A root-removal effort based on hand-picking visible roots reduced the radiocarbon content and increased the estimated turnover time of the light fraction by roughly 12%. Root-removal protocols that vary between investigators thus can potentially confound variability in carbon cycling for this fraction caused by environmental factors, such as climate. Ultrasonic dispersion did not have a clear effect on the light fraction C and N content or isotopic signature, but led to a decrease in the % C and C/N of the recovered heavy fractions, and losses of 12–19% of the total soil C to the sodium metatungstate density solution.

Sequentially isolated density fractions clearly differed in mineralogy and organic matter chemistry, but natural-abundance 14C analyses indicated that distinct mineral phases did not correspond to unique C-turnover pools. Density fractions containing kaolinite group minerals alone and in combination with hydroxy-interlayered vermiculite were found to harbor both fast and slow cycling carbon. In contrast, severe chemical treatment isolated a carbon pool with the lowest overall 14C content and longest inferred mean turnover time. Overall, our results show that care must be taken when relying on physical (density) separation to isolate soil fractions with different dynamics, as the details of treatment will influence the results.

This paper reports the first ages determined in the C14 Dating Laboratory of the Geological Survey of Canada. The C14 dating program of the Geological Survey is a cooperative project; geologists of the Pleistocene Section assess and select samples for dating, and the Isotope and Nuclear Research Section, under Dr. R. K. Wanless, developed and operates the laboratory and calculates ages. The first part of this paper, devoted to sample preparation, counting procedure, and interlahoratory check dates was prepared by the first author, who built and operates the laboratory. The date list was compiled by the second author from descriptions of samples and interpretations of dates provided by various collectors. Most samples analyzed so far have originated within the Geological Survey.

Archaeologists working in the Belize Valley have argued for the persistence of Maya populations from the Classic (AD 300–900) through Postclassic (AD 900–1500) periods since Gordon Willey's groundbreaking settlement survey and excavation work in the 1950s. This is contrary to the trajectory recorded in some parts of the Maya region where there is clear evidence for political disruption and population decline at the end of the Classic period. The argument for continuous Classic to Postclassic occupation in the Belize Valley remains ambiguous due to researchers' reliance on relative ceramic chronologies. This article reports the results of direct accelerator mass spectrometry (AMS) radiocarbon dating of human skeletons (n = 12) from the important center of Baking Pot, Belize, which is thought to provide some of the best ceramic evidence for continuity in the valley. The AMS dates show a long span of mortuary activity between the Middle Preclassic and Late Classic periods (405 cal BC to cal AD 770), with a hiatus in activity during the Early Postclassic (cal AD 900–1200) and subsequent activity in the Late Postclassic (cal AD 1280–1420). These results are not consistent with the idea that Baking Pot was occupied continuously from the Classic through Postclassic periods. This work highlights the need for additional AMS 14C work at Baking Pot and elsewhere to establish absolute chronologies for evaluating the political and demographic collapse of Classic Maya regional centers.

When and where the process of state formation took place in the biblical kingdom of Judah is heavily debated. Our regional project in the southwestern part of Judah, carried out from 2007 to the present, includes the excavation of three Iron Age sites: Khirbet Qeiyafa, Tel Lachish, and Khirbet al-Ra’i. New cultural horizons and new fortification systems have been uncovered, and these discoveries have been dated by 59 radiometric determinations. The controversial question of when the kingdom was able to build a fortified city at Lachish, its foremost center after Jerusalem, is now resolved thanks to the excavation of a previously unknown city wall, dated by radiocarbon (14C) to the second half of the 10th century BCE.

We present pollen diagrams and sedimentological analyses from a lake site within an extensive dune system on the Aupouri Peninsula, Northland. Five thousand years ago, a regional Agathis australis–podocarp-broadleaf forest dominated the vegetation, which manifested an increasing preponderance of conifer species. Climate was cooler and drier than at present. From ca. 3400 bp, warmth-loving species such as A. australis and drought-intolerant species, Dacrydium cupressinum and Ascarina lucida, became common, implying a warm and moist climate. The pollen record also suggests a windier climate. The most significant event in the record, however, occurred after ca. 900 bp (800 cal bp) when anthropogenic deforestation commenced. A dramatic decline in forest taxa followed, accompanied by the establishment of a Pteridium–esculentum-dominated community. Fire almost certainly caused this, evidenced by a dramatic increase of charcoal. Sedimentological evidence for this site indicates a relatively stable environment before humans arrived and an increasingly unstable environment with frequent erosional events after human contact.

This list contains the results of measurements madeduring 1965 and 1966. Samples are counted in theform of acetylene gas, as previously, and agescomputed on the basis of the Libby half-life, 5568 ±30 yr. The error listed is always larger than theone-sigma statistical counting error commonly used,takes into account known uncertainty laboratoryfactors, but does not include external (field oratmospheric) variations.

We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150–1000°C; 5°C×min–1) to be (3.7±0.6) μg C with an Fm value of 0.555±0.042 and a δ13C value of (–29.0±0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and δ13C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk δ13C values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent 13C depletion within the RPO instrument (mean–bulk: μ=–0.8‰; ±1σ=0.9‰; n=66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean–bulk: μ=0.005; ±1σ=0.014; n=36). Lastly, we show there exists no significant intra-sample δ13C variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between 13C- and 12C-containing compounds (13–12∆E) of 0.3–1.8 J×mol–1, indicating that blank and mass-balance corrected RPO δ13C values accurately retain carbon source isotope signals to within 1–2‰.

14C and δ13C values of C-containing species in cave drip waters are mainly controlled by the C isotope composition of karst rock and soil air, as well as by soil carbon dynamics, in particular the amount of soil CO2 in the unsaturated soil zone and the process of calcite dissolution. Here, we investigate soil carbon dynamics by analyzing the 14C activity and δ13C values of C dissolved in cave drip water. Monthly over a 2-yr period, we collected drip water from 2 drip sites, one fast and one relatively slow, within the shallow Grotta di Ernesto Cave (NE Italy). The 14C data reveal a pronounced annual cycle. In contrast, the δ13C values do not show an annual pattern and only small interannual variability compared to the δ13C values of soil waters. The annual 14C drip-water cycle is a function of drip-rate variability, soil moisture, and ultimately hydrology.

The following list shows the age measurements carried out at Saclay by the Service d'Electronique Physique, using the C14 method.

The apparatus employed was completed and calibrated in 1956 and the first tests were performed during the same year. The counting unit is a 1.2 L stainless steel proportional counter and the filling gas is pure CO2 at 74 cm Hg pressure. The shield consists of 20 cm of lead, 10 cm of iron, a coincidence ring and 2 cm of bismuth. The background is 4.86 ± 0.05 counts/min. (Error is ± σ, the duration of each counting being 24 hours.) Final purification is performed by adsorption of CO2 on alumina at low temperature, followed by desorption at room temperature; this has proved particularly effective and gives a very good filling gas. Technique was described in detail previously by the authors (Perquis, Delibrias, and David, 1956; Delibrias and Perquis, 1958).

As a modern carbon standard we first used wood taken from the 1930 to 1945 rings of a large Douglas fir; this standard gave a net count of 6.02 counts/min. This activity, taking into account a 2% Suess-effect for this wood, was found to be 95% of the activity of the NBS oxalic-acid standard, measured in the same counter.

The NBS standard has been adopted by this laboratory since January 1961, and values given here are calculated from this new standard.

Measurements listed are dates obtained from 1956 through 1962. No reports are given here from other types of measurements carried out at Saclay, such as: (1) C14 content of wild plants growing in the vicinity of nuclear reactors; (2) measurement of C14 in blood proteins of workers of the radioactive-tracers industry; (3) Spallation cross-sections for C14 production in oxygen and iron by high energy protons; (4) C14 content of meteorites.

The Aquia (Paleocene) and Magothy (Late Cretaceous) Formations of the Atlantic Coastal Plain represent two well-characterized (hydrodynamically and geochemically) aquifers in southern Maryland. 14C measurements of the dissolved organic (DOC) and inorganic carbon (DIC) of Aquia and Magothy groundwaters have been made using accelerator mass spectrometry (AMS). Both DI14C and DO14C concentrations in the initial flow path are unexpectedly low. As the water progresses farther from the recharge area, the DI14C percent modern carbon (pMC) is consistently lower than the DO14C pMC; this difference stays constant for all samples. The 14C-derived ages for an Aquia water sample downgradient at Site 4 are 17 ka and 12 ka for DI14C and DO14C, respectively. Radiocarbon ages have been compared to ages determined by two other independent dating methods: computer-simulated hydrodynamic modeling and age estimates based on changes in Cl−, 18O and 2H distributions, which are interpreted to be influenced by sea level and climate.

The following list of dates contains all measurements made during 1972, i.e., since our last list. Counting equipment, operating procedures and sample pretreatment are the same as previously described (R., 1969, v. 11, p. 263). Age calculations are based on 95% activity of the NBS oxalic acid standard computed from the Libby half-life of 5570 ± 30 yr. Background samples are synthesized from Welsh anthracite. Errors quoted refer only to the standard deviation (1σ) calculated from a statistical analysis of sample, background and standard count rates.

We measured airborne releases of 14C from the Paks Pressurized Water Reactor (PWR) Nuclear Power Plant (NPP). Two continuous stack samplers collect 14C in 14CO2 and 14CnHm chemical forms. 14C activities were measured using two techniques; environmental air samples of lower activities were analyzed by proportional counting, stack samples were measured by liquid scintillation counting. 14C concentration of air in the stack varies between 80 and 200 Bqm−3. The average normalized yearly discharge rates for 1988–1993 were 0.74 TBqGW−1ey−1 for hydrocarbons and 0.06 TBqGW−1ey−1 for CO2. The discharge rate from Paks Nuclear Power Plant is about four times higher than the mean discharge value of a typical Western European PWR NPP. The higher 14C production may be apportioned to the higher level of nitrogen impurities in the primary coolant. Monitoring the long-term average excess from the NPP gave D14C = 3.5‰ for CO2 and D14C = 20‰ for hydrocarbons. We determined 14C activity concentration in the primary coolant to be ca. 4 kBq liter−1. The 14C activity concentrations of spent mixed bed ion exchange resins vary between 1.2 and 5.3 MBqkg−1 dry weight.

Dates listed below are based on measurements made from June 1968 to May 1970 by the liquid scintillation technique using benzene. In general, the experimental procedure is as described previously (Barker, Burleigh, and Meeks, 1969a) with a few changes in detail. Data are now processed by computer using a comprehensive Algol program written by Andrew Barker, King's College, Univ. of London. There is no need to standardize on any particular sample weight and, as the benzene synthesizer can also deal with samples in the range up to the equivalent of 9 gm of carbon in a single synthesis, the amount of sample available is now less critical. However, for older material, a minimum of 1 gm of carbon is required. Another factor contributing to efficiency of operation is the “bomb” technique for sample combustion (Barker, Burleigh, and Meeks, 1969b), also mentioned in the previous date list. Finally, during 1969, an MS20 double collection mass spectrometer was acquired and all dates (but not all those in this list) are now corrected for isotopic fractionation.

14C dating with the new Vienna Environmental Research Accelerator (VERA) began with the age determination of a mummified marmot found in the Austrian Alpine region. Soft tissue and bones of the marmot were used for the investigation. For comparison, bone material from known-age samples was also processed and measured. These exercises showed that 14C dating with VERA is reliable, and since that time various samples from archaeological context have been dated.

We also studied the applicability of the 14C method in forensic sciences to determine the time of death of human individuals. 14C/12C measurements of samples from different organic human material (bone collagen, lipids from bone and bone marrow, hair) were performed and compared with the tropospheric “bomb peak” values to transform the measured ratios into “calibrated ages”. For specific substances with rapid turnover rates, this gives an estimate for the time of death of the individual. In our study, lipids and hair yield reasonable times of death, whereas the collagen fraction from bones, which has a relatively long turnover time, is not suitable for this purpose.